For the past several years, the conventional approach for matching a high Q impedance (e.g., an antenna) to a real impedance (e.g., a transmitter) has utilized an L network with two independently controlled reactive matching elements in series and shunt arms of the network. Phase and impedance detectors control two separate closed loop servo systems. This approach is relatively expensive as it requires separate variable reactors with control and driving mechanisms for each, generally including a motor, tachometer-generator, servo amplifier, and gearing, or separate binary controllers for each reactor. Further, with many systems it is necessary to initialize the variable reactances of the network, which can cause complex and expensive hardware.
Examination of the values of a variable reactive element on the matched (e.g., transmitter) side of the L network indicates that it does not have to be adjusted very accurately if a variable reactive component on the unmatched load (e.g., antenna) side is carefully controlled. This property permits the matching element on the matched side to be preset either (1) as a function of frequency information, or (2) in unison with adjustment of the variable component on the load side of the network. Use of either of these techniques reduces the servo system complexity by nearly a factor of two, to provide a reduction in size and cost, while increasing reliability.